1. Field of the Invention
The present invention relates to a polarity switching signal generator able to stably generate a suitable tracking error signal, a method of the same, and an optical disk drive.
2. Description of the Related Art
Digital versatile disk-random access memory (DVD-RAM) and other rewritable optical disks are now in use.
Such rewritable optical disks include ones which use for example a land groove system as a disk format. In this case, the recording surface of the optical disk is provided with data areas in which only guide grooves for recording and reproducing any information and address areas in which absolute positions on a disk are stored by pits.
The formats of the land-groove system can be roughly divided in a double spiral format and a single spiral format.
In the double spiral format, as shown in FIG. 1, a land track 50 and a groove track 51 are located next to each other. Further, in the single spiral format, as shown in FIG. 2, a land track 52 and a groove track 53 are located one after the other for every circuit to form one track as a whole.
Below, the tracking servo control of a recording and reproduction apparatus of the related art for recording and reproducing data to and from a DVD-RAM of the single spiral format will be explained.
FIG. 3 is a block diagram of an optical disk drive 1 of the related art for realizing the tracking servo control of a recording and reproduction apparatus of a DVD-RAM disk.
As shown in FIG. 3, in the optical disk drive 1, a DVD-RAM disk 2 is driven to rotate by a spindle motor 15. A laser beam from a laser 3 is fired through an object lens to a position on the recording surface of the DVD-RAM disk 2 under the control of a tracking coil 4. The reflected laser beam is received by a photoreceptor 5.
The photoreceptor 5 converts the reflected laser beam from the DVD-RAM disk 2 to a tracking error signal S5a indicating the deviation of tracking and a sum signal S5b indicating the amount of the light of the reflected laser beam and outputs these to A/D converters 6 and 7 respectively.
The tracking error signal S5a and the sum signal S5b are converted to a digital tracking error signal S6 and a sum signal S7 and output to a normalizer 8.
The normalizer 8 normalizes the tracking error signal S6 so that its level does not change and outputs the normalized tracking error signal S8 to a polarity switch 9.
On the other hand, the address S5c read from the DVD-RAM disk 2 is output from the photoreceptor 5 to the last sector detector 13. The last sector detector 13 detects a last sector signal S13 indicating a sector just before the land and the groove are switched on the basis of address S5c.
Next, a one-sector delay unit 14 delays the last sector signal S13 by exactly one sector's worth of time to produce a polarity switching signal S14 and outputs the polarity switching signal S14 to the polarity switch 9.
Based on the polarity switching signal S14, the polarity switch 9 inverts the polarity of the tracking error signal S8 in accordance with need to produce a tracking error signal S9 of a controlled polarity. It outputs the tracking error signal S9 to a phase compensation digital filter 10.
It is necessary to control the polarity of the tracking error signal SB in this way because the polarity of the tracking error signal becomes inverted between when tracing a land and when tracing a groove.
The tracking error signal S9 is phase-compensated and converted to an analog signal in the D/A converter 11 to produce a drive signal S11.
The drive signal S11 is amplified by a drive amplifier, then output to the tracking coil 4 as a drive signal S12 to drive the tracking coil 4.
Summarizing the problems to be solved by the invention, in the optical disk drive 1 of the related art shown in FIG. 3, as describe below, the polarity switching signal S14 is not suitably produced, so if suffers from the disadvantage that the tracking servo control becomes unstable.
Specifically, when the recording surface of the DVD-RAM disk 2 becomes dirty and the last sector cannot be detected, when starting to trace a track after a seek operation, when using a zoned constant linear velocity (CLV) format where the number of the address areas 60 present in one turn of the disk differs for each zone as shown in FIG. 4 and the rotating speed of a spindle motor 15 will not stabilize at the point of change of zones, etc. the polarity switching signal S14 is not suitably produced.
Note that in a DVD-RAM of the CAV format, as shown in FIG. 5, the address areas 70 and the data areas 71 are arranged radially.
When the polarity switching signal S14 is not suitably produced and the timing of the polarity switching becomes off, a suitable tracking error signal S9 is not produced while the polarity is wrong and the tracking servo control becomes unstable state.
Further, during a seek operation, since an optical pick-up is moving over the tracks, the last sector cannot be detected and the polarity cannot be suitably controlled in the polarity switch 9. Therefore, during a seek operation, the tracking error signal S9 becomes discontinuous at the boundary between a land and a groove, so there is the disadvantage that a count error occurs in the traverse counter which counts the number of tracks being traversed.